Expedited processing is available for visas issued in Singapore, but the price is higher for such service. (And visas are more expensive for Americans than most others.) Only word of warning is to get in early (i.e., at least two hours before posted closing time for visa issuance) so that the staff can't tell you that they can't do it until tomorrow. Generally, the PRC visa process in SIN goes very smoothly as long as you have the form filled out correctly, have any supporting documentation (if needed), have the photo(s), and the funds in local currency with you.